This invention relates generally to turbine engines and more particularly, to methods and apparatus for assembling gas turbine engines.
Known gas turbine engines include combustors which ignite fuel-air mixtures which are then channeled through a turbine nozzle assembly towards a turbine. At least some known turbine nozzle assemblies include a plurality of arcuate nozzle segments arranged circumferentially. At least some known turbine nozzles include a plurality of circumferentially-spaced hollow airfoil vanes coupled by integrally-formed inner and outer band platforms. More specifically, the inner band forms a portion of the radially inner flowpath boundary and the outer band forms a portion of the radially outer flowpath boundary.
Within known engine assemblies, an interface defined between the turbine nozzle and an aft end of the combustor is known as a fish-mouth seal. More specifically, within such engine assemblies, leading edges of the turbine nozzle outer and inner band platforms are generally axially aligned with respect to a leading edge of each airfoil vane extending therebetween. Accordingly, in such engine assemblies, when hot combustion gases discharged from the combustor approach the nozzle vane leading edge, a pressure or bow wave reflects from the vane leading edge stagnation and propagates a distance upstream from the nozzle assembly, causing circumferential pressure variations across the band leading edges and a non-uniform gas pressure distribution. The pressure variations may cause localized nozzle oxidation and/or localized high temperature gas injection, each of which may decrease engine efficiency. Moreover, such pressure variations may also cause the vane leading edge to operate at an increased temperature in comparison to the remainder of the vane.